fix: show raw PHP response in error message, clean up errores column UI

- sync_paciente: catch JSONDecodeError separately and include HTTP status
  + first 300 chars of raw response so PHP errors are visible in the log
- envios_erp.html: Errores column shows count only (not all inline messages)
  — error detail is already visible in the expandable Ver N row

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/services/whatsapp_sync.py

@@ -145,7 +145,17 @@ async def sync_paciente(
             async with httpx.AsyncClient(timeout=15) as c:
                 resp = await c.post(url, json=payload, headers=headers)
 
-        data = resp.json()
+        try:
+            data = resp.json()
+        except Exception as json_err:
+            raw = resp.text[:300].strip()
+            return {
+                "ok":      False,
+                "action":  "error",
+                "message": f"HTTP {resp.status_code} — respuesta no JSON: {raw!r}",
+                "doc":     payload["numero_documento"],
+                "nombre":  payload["nombre_completo"],
+            }
         return {
             "ok":      data.get("ok", False),
             "action":  data.get("action", ""),